IB/cm: Check LAP state before sending an MRA

NULL pointer dereferences in ib_cm_init_qp_attr() were seen by some
users.  From a crash dump, I determined that we died in
cm_init_qp_rts_attr() (it's inlined, so it doesn't show up in the
traceback) on the line labeled below:

static int cm_init_qp_rts_attr(struct cm_id_private *cm_id_priv,
                               struct ib_qp_attr *qp_attr,
                               int *qp_attr_mask)
{
        ........
        if (cm_id_priv->id.lap_state == IB_CM_LAP_UNINIT) {
                .....
        } else {
               *qp_attr_mask = IB_QP_ALT_PATH | IB_QP_PATH_MIG_STATE;
               qp_attr->alt_port_num = cm_id_priv->alt_av.port->port_num; <-die


The problem is that the rdma_cm can call ib_send_cm_mra() after a
connection has been established.  The ib_cm incorrectly assumes that
the MRA is in response to a LAP (load alternate path) message, even
though no LAP message has been received.  The ib_cm needs to check the
lap_state before sending an MRA if the cm_id state is established.

Reported-by: Arthur Kepner <akepner@sgi.com>
Reported-by: Josh England <jjengla@gmail.com>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/cm.c

@@ -2409,10 +2409,12 @@ int ib_send_cm_mra(struct ib_cm_id *cm_id,
 		msg_response = CM_MSG_RESPONSE_REP;
 		break;
 	case IB_CM_ESTABLISHED:
-		cm_state = cm_id->state;
-		lap_state = IB_CM_MRA_LAP_SENT;
-		msg_response = CM_MSG_RESPONSE_OTHER;
-		break;
+		if (cm_id->lap_state == IB_CM_LAP_RCVD) {
+			cm_state = cm_id->state;
+			lap_state = IB_CM_MRA_LAP_SENT;
+			msg_response = CM_MSG_RESPONSE_OTHER;
+			break;
+		}
 	default:
 		ret = -EINVAL;
 		goto error1;